continental drift - National Geographic Society continental drift The way some continents fit together like puzzle pieces inspired the theory of continental drift. Map by USGS Urkontinent Alfred Wegener’s original name for his proposed, ancient continent was “Urkontinent”—ur meaning “first or original,” and kontinent meaning “continent” in Wegener’s native language, German. A more popular name for this huge ancient landmass is Pangaea, which means “all lands” in Greek. Colliding Skyward The collision of the Indian subcontinent and Asian continent created the Himalayan mountain range, home to the world's highest mountain peaks, including 30 that exceed 7300 meters (24,000 feet). Because continental drift is still pushing India into Asia, the Himalayas are still growing. Continental drift describes one of the earliest ways geologist s thought continent s moved over time. Today, the theory of continental drift has been replaced by the science of plate tectonics . The theory of continental drift is most associated with the scientist Alfred Wegener .

In the early 20th century, Wegener published a paper explaining his theory that the continental landmass es were “drifting” across the Earth, sometimes plowing through oceans and into each other. He called this movement continental drift. Pangaea Wegener was convinced that all of Earth’s continents were once part of an enormous , single landmass called Pangaea . Wegener, trained as an astronomer , used biology , botany , and geology describe Pangaea and continental drift. For example, fossil s of the ancient reptile mesosaurus are only found in southern Africa and South America. Mesosaurus, a freshwater reptile only one meter (3.3 feet) long, could not have swum the Atlantic Ocean. The presence of mesosaurus suggests a single habitat with many lakes and rivers. Wegener also studied plant fossils from the frigid Arctic archipelago of Svalbard, Norway. These plants were not the hardy specimen s adapt ed to survive in the Arctic climate . These fossils were of tropical plants, which are adapted to a much warmer, more humid environment. The presence of these fossils suggests Svalbard once had a tropical climate .

Finally, Wegener studied the stratigraphy of different rocks and mountain range s. The east coast of South America and the west coast of Africa seem to fit together like pieces of a jigsaw puzzle , and Wegener discovered their rock layers “fit” just as clearly. South America and Africa were not the only continents with similar geology. Wegener discovered that the Appalachian Mountains of the eastern United States, for instance, were geologically related to the Caledonian Mountains of Scotland. Pangaea existed about 240 million years ago. By about 200 million years ago, this supercontinent began breaking up. Over millions of years, Pangaea separated into pieces that moved away from one another. These pieces slowly assumed their positions as the continent we recognize today. Today, scientists think that several supercontinents like Pangaea have formed and broken up over the course of the Earth’s lifespan. These include Pannotia, which formed about 600 million years ago, and Rodinia, which existed more than a billion years ago. Tectonic Activity Scientists did not accept Wegener’s theory of continental drift.

One of the elements lacking in the theory was the mechanism for how it works—why did the continents drift and what patterns did they follow? Wegener suggested that perhaps the rotation of the Earth caused the continents to shift towards and apart from each other. (It doesn't.) Today, we know that the continents rest on massive slab s of rock called tectonic plate s. The plates are always moving and interacting in a process called plate tectonics. The continents are still moving today. Some of the most dynamic sites of tectonic activity are seafloor spreading zones and giant rift valleys. In the process of seafloor spreading , molten rock rises from within the Earth and adds new seafloor ( oceanic crust ) to the edges of the old. Seafloor spreading is most dynamic along giant underwater mountain ranges known as mid-ocean ridge s. As the seafloor grows wider, the continents on opposite sides of the ridge move away from each other. The North American and Eurasian tectonic plates, for example, are separated by the Mid-Atlantic Ridge . The two continents are moving away from each other at the rate of about 2.5 centimeters (1 inch) per year.

Rift valley s are sites where a continental landmass is ripping itself apart. Africa, for example, will eventually split along the Great Rift Valley system . What is now a single continent will emerge as two—one on the African plate and the other on the smaller Somali plate. The new Somali continent will be mostly oceanic, with the Horn of Africa and Madagascar its largest landmasses. The processes of seafloor spreading, rift valley formation, and subduction (where heavier tectonic plates sink beneath lighter ones) were not well-established until the 1960s. These processes were the main geologic forces behind what Wegener recognized as continental drift. Term to adjust to new surroundings or a new situation. Alfred Wegener (1880-1930) German meteorologist and geologist. ancient person who studies space and the universe beyond Earth's atmosphere. biology always changing or in motion. enormous having to do with a habitat or ecosystem of a lake, river, or spring. frigid person who studies the physical formations of the Earth. geology Noun study of the physical history of the Earth, its composition, its structure, and the processes that form and change it.

Great Rift Valley system Noun series of faults and other sites of tectonic activity stretching from southwestern Asia to the Horn of Africa. habitat strong or able to withstand severe weather. humid air containing a large amount of water vapor. jigsaw puzzle interlocking pieces that, when correctly put together, display a picture or design. landmass process or assembly that performs a function. mesosaurus freshwater reptile that lived during the early Permian period, about 300 million years ago. Mid-Atlantic Ridge underwater mountain range that runs from Iceland to Antarctica. mid-ocean ridge solid material turned to liquid by heat. mountain range series or chain of mountains that are close together. oceanic crust thin layer of the Earth that sits beneath ocean basins. Pangaea supercontinent of all the Earth's landmass that existed about 250 million years ago. plate tectonics movement and interaction of the Earth's plates. reptile animal that breathes air and usually has scales. rift valley flat, thick piece of material such as earth or stone. specimen individual organism that is a typical example of its classification. stratigraphy study of rock layers and layering.

subduction process of one tectonic plate melting, sliding, or falling beneath another. supercontinent ancient, giant landmass that split apart to form all the continents we know today. tectonic plate Noun massive slab of solid rock made up of Earth's lithosphere (crust and upper mantle). Also called lithospheric plate. tropical Adjective existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south. tropical climate Continental Drift Next page Continental Drift The most important feature of the crust is that it is not stable. It is a constantly changing stage upon which this drama will be unfolded, and the scene-shifter in this great theatre is called continental drift. At some stages in history, the continents have been assembled into huge �supercontinents� which over millions of years are then broken apart into smaller fragments. These drift around until they are once more re-assembled but into a different configuration. Each cycle takes between 300 to 600 million years. We are not sure when this process began. Continental drift squashes and changes the continents so much that it is very hard to work out their early history.

Continental drift is still happening today and is important because it causes volcanic eruptions, earthquakes and tsunamis. Some people also think that it is one cause of ice ages . Today the theory of plate tectonics, which includes continental drift, forms a framework for the study of geology and the Earth. For the evidence that continental drift is happening, click here . It is the heat generated by radioactive decay inside the Earth which drives this process. The center of the Earth contains uranium and other heavy atoms which decay, releasing energy. That is why the Earth�s core is hot. Hot rock in the core turns to a viscous liquid (magma) which can rise up through the cooler rocks above. Magma rises up through the mantle and spreads out on the surface to form the ocean floor. As the ocean floor spreads it pushes the continents ahead. They move one or two centimeters each year. Mountains and Volcanoes As the continents move around they sometimes hit each other, creating mountains. This is how the Alps and the Himalayas were created. Mountains like this are on the inside of continents. Sometimes continents do not hit head on, but rub past each other.

Since they do not have smooth edges, the rubbing is jerky and uneven. Pressure builds up and is then suddenly released. This creates earthquakes. The San Andreas Fault in California is an example of this. Volcanoes formed by Continental Drift On the Earth today, volcanoes are mainly formed by continental drift. As lighter continental rocks are pushed over heavier oceanic ones, friction melts the rock which rises and produces a volcano. Volcanoes formed by continental drift Such volcanoes are often found near the edges of continents. As it sinks it melts and hot rock rises up, creating volcanoes along the coast. The Andes are being created in this way. Sometimes the volcanoes lie in an arc just off the coast of a continent. The islands of Japan are being formed like this. Vaalbara Supercontinent 3.6 to 2.1 bya We have little idea what the continents looked like during the Archaean Era, but it seems that parts of what is now Africa and Australia were once assembled into a supercontinent called Vaalbara. It seems to have been assembled by continental drift between about 3.6 bya and 3.1 bya, during the Archaean Era .

It was then broken apart between about 2.7 and 2.1 bya. Archaean Climate Various theories exist about the climate during the Archaean. Some claim it was hot, others say warm and some think it was cold. The warm theory is partly based on the fact that, for the molecules of life to be formed, a source of energy would be necessary. Dive and Discover : History of Oceanography History of Oceanography Click on the arrows below to learn more Continental Drift and Seafloor Spreading The Keys to Modern Earth and Oceanographic Sciences Deeper Discovery Until only recently, geologists had thought that Earths surface hadnt changed much since the planet formed 4.6 billion years ago. They believed that the oceans and continents were always where they are now. But less than 100 years ago, a German scientist named Alfred Wegener took notice of some interesting findings. Similar plant and animal fossils were found in both Africa and South America and on other continents separated by oceans. Similar rock formations were also found on distant continents. This suggested that the formations were once whole and later divided. Alfred Wegener was born in Berlin, Germany on November 1, 1880.

He spent a great deal of time in Greenland as part of several exploration and research expeditions. His book The Origin of Continents and Oceans was originally published in Germany in 1929 and was instrumental in the development of the theory of seafloor spreading. Wegener died on the ice in Greenland in Nov. 1930. Wegener also noticed that if you could shove western Europe and Africa together with North and South America, their coastlines would fit together very neatly. All this evidence led Wegener to believe that the continents were once connected but had separated and drifted apart. In 1915, Wegener proposed his continental drift theory. He said that the continents floated atop the mantle-a heavier, denser layer of rocks deep within the earth. Wegener predicted that heat rising within the hot mantle created currents of partially melted rocks that could move the continents around the earths surface. Like many revolutionary theories, Wegeners was not initially accepted by scientists. The good fit of the continents and the fossil and rock evidence did not provide enough proof.

For decades afterward, scientists still did not understand how massive continents could be transported across the face of the Earth, and they had no evidence of any process that could cause continents to move. In the 1950s and 1960s, marine geologists such as Bruce Heezen, Marie Tharp, and Henry Menard used data from echo sounders to map ocean ridges in the North Atlantic and the Pacific. They noticed first that these ridges stretched on for thousands of kilometers in long, continuous mountain chains that wound around the Earths surface, almost like the stitches on a baseball. The scientists also observed that the crest of the ridges had a topography that closely resembled volcanic rift zones on land. At their crests, they had V-shaped central valleys with steep faults on either side. This evidence led early marine geologists to deduce that the mid-ocean ridges were formed by seafloor volcanoes. Reconstruction of the map of the world according to drift theory for three epochs, the upper one is the upper Carboniferous, the middle one is for the Eocene, and the lower one is for the Lower Quaternary.

The dotted areas on the continents are areas where shallow seas existed during those time periods. This figure appears as Figure 4 in Wegeners book. When these volcanoes erupted, they spewed out lava that cooled and solidified to become new seafloor. It was soon discovered that when this lava cooled, magnetic particles within it aligned with Earths magnetic field. After World War II, when magnetometers began to be used to survey the seafloors magnetic properties, scientists were surprised to learn that Earths magnetic field had flip-flopped many times over its history, with the north and south poles exchanging places! So depending on when seafloor rocks were formed, their particles are aligned in either one direction or the other, and they are said to have either positive or negative magnetic anomalies. In the late 1960s, magnetometer data revealed an alternating striped pattern of seafloor rocks. Rocks that formed when Earths magnetic field was in one position alternated with rocks that formed when the field was reversed. The stripes ran parallel to the mid-ocean ridges and extended out hundreds of miles on either side of them.

The seafloors permanent magnetic signatures showed that new ocean crust was created at the ridge crests and then spread outward in both directions. This seafloor spreading hypothesis had been proposed a few years earlier by Harry Hess, a petrologist at Princeton University, and Robert Dietz, an oceanographer in the US Coast and Geodetic Survey (the federal department that made maps of the oceans and US coastlines). Hess went on to say that as the ocean crust spreads and cools over millions of years, it becomes denser and eventually sinks down into oceanic trenches, or subduction zones, a long way from where it forms at the mid-ocean ridge crest. As ocean crust descends toward the hot mantle, it melts and becomes recycled into the mantle. Volcanoes and earthquakes are common in subduction zones, which often occur at the edges, or margins, of continents. The Rim of Fire, which is named for its volcanoes and earthquakes, is created by a series of subduction zones along the coastlines surrounding the Pacific Ocean-from western South and Central America to the Aleutian Islands in Alaska, down the western Pacific, from Japan and the Philippines, all the way to Indonesia and New Zealand.

In 1965, a Canadian geophysicist, J. Tuzo Wilson, combined the continental drift and seafloor spreading hypotheses to propose the theory of plate tectonics. Tuzo said that Earths crust, or lithosphere, was divided into large, rigid pieces called plates. These plates float atop an underlying rock layer called the asthenosphere. In the asthenosphere, rocks are under such tremendous heat and pressure that they behave like a viscous liquid (like very thick honey). The term continental drift was no longer fully accurate, because the plates are made up of continental and oceanic crust, which both drift over Earths face. Tuzo Wilson predicted three types of boundaries between plates: mid-ocean ridges (where ocean crust is created), trenches (where the ocean plates are subducted) and large fractures in the seafloor called transform faults, where the plates slip by each other. Plate tectonics has provided a unifying theory that explains the fundamental processes that shape the face of the Earth.

© 2005 Dive and Discover is a registered trademark of Woods Hole Oceanographic Institution Continental Drift - AS Geography Flashcards - Cram.com the theory that the continental landmasses have changed position over time. What is the geological evidence for continental drift? The way in which continents (e.g. South America and Africa)appear to fit together. Especially when you look at the continental shelf rather than the present coastline. Rock types and geological structures are similar on both sides of the Atlantic. E.g. The Appalachian Mountains (N.America) and the Caledonian Mountains (Scotland) both have the same sequence of igneous and sedimentary rocks. What biological evidence for continental drift is there? Some fossils (e.g. Mesosaurus) are found in both SW.Africa and Brasil - landmasses wre joined and creatures lived in the whole combined area Fossils of a fern (Glossopteris) are found widely across the southern continents. Fossils of Triassic period reptiles have been found in areas which are now far apart. E.g. Cynagnathus in S.America and Africa. What is the Climatological evidence for continental drift?

The coal and oil reserves found in Antatrtica suggests that this area was once in a different climatic zone. Glacial striations in Brazil and W.Africa Gklacial deposits in India, South Americal and the Vaal Valley in South Africa. These landmarks suggest that the areas once had very simelar climatic conditions even though they are now far apart and in very different climatic zones. According to Wegener, what was Earth like 300 million years ago? All the continents were joined together 300 million years ago as a single supercontinent caleed Pangaea According to Wegener, what was happening to the tectonic structure of Earth 200 million years ago? The continents drifted apart. This formed: -a northern hemishere aseemblage known a Laurasia comprising of Eurasia and North America. - A Southern hemisphere group called Gondwanaland consisting of Africa, Australasia, India, South America and Antartica Why was Wegener's theory not widely accepted? -He was not a meteorologist - He could not explain how or why the plates moved (He did have some suggestions though - centrifugal force and the gravitational force of the moon).

What is the plate tectonic theroy? The Earth's crust is divided into several major and a number of smaller plates of relatively rigid crust material. The plates move in realtion to each other, riding on the weak, soft and partially molten rocks beneath. What evidence is there for sea-floor spreading and plate tectonic movement? The basaltic rocks near the mid atlantic ridge are much newer than those found near the continental shelves. This is evidence that rocks were formed at the ridge and have then moved apart being replaced by new rocks which form at the ridge. how does the palaeomagnetism of basalt rocks suggest that rock has been formed at a ridge and then moved apart? There is a parallel pattern of magnetism in the rocks. this develops because, as the magma cools and solidifies, the metallic elements within it are magnetised in the direction of the Earth's magnetic field. There have been many reversals of the earth's magnetic field over time - The pattern of magnetism found in the rocks relates to the alternating pattern of of northely and southerly magnetism of the earth's magnetic field. What is the mechanism for the movement of the tectonic plates? Convection currents beneath the earth's surface.

Cram has partnered with the National Tutoring Association Claim your access Ready To Get Started? Alfred Wegener Alfred Wegener (1880-1930) "Scientists still do not appear to understand sufficiently that all earth sciences must contribute evidence toward unveiling the state of our planet in earlier times, and that the truth of the matter can only be reached by combing all this evidence. . . It is only by combing the information furnished by all the earth sciences that we can hope to determine 'truth' here, that is to say, to find the picture that sets out all the known facts in the best arrangement and that therefore has the highest degree of probability. Further, we have to be prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we draw." Alfred Wegener. The Origins of Continents and Oceans (4th edition) Some truly revolutionary scientific theories may take years or decades to win general acceptance among scientists.

This is certainly true of plate tectonics , one of the most important and far-ranging geological theories of all time; when first proposed, it was ridiculed, but steadily accumulating evidence finally prompted its acceptance, with immense consequences for geology, geophysics, oceanography, and paleontology. And the man who first proposed this theory was a brilliant interdisciplinary scientist, Alfred Wegener. Born on November 1, 1880, Alfred Lothar Wegener earned a Ph.D in astronomy from the University of Berlin in 1904. However, he had always been interested in geophysics, and also became fascinated with the developing fields of meteorology and climatology. During his life, Wegener made several key contributions to meteorology: he pioneered the use of balloons to track air circulation, and wrote a textbook that became standard throughout Germany. In 1906 Wegener joined an expedition to Greenland to study polar air circulation. Returning, he accepted a post as tutor at the University of Marburg, taking time to visit Greenland again in 1912-1913. (The above photograph of Wegener was taken during this expedition).

In 1914 he was drafted into the German army, but was released from combat duty after being wounded, and served out the war in the Army weather forecasting service. After the war, Wegener returned to Marburg, but became frustrated with the obstacles to advancement placed in his way; in 1924 he accepted a specially created professorship in meteorology and geophysics at the University of Graz, in Austria. Wegener made what was to be his last expedition to Greenland in 1930. While returning from a rescue expedition that brought food to a party of his colleagues camped in the middle of the Greenland icecap, he died, a day or two after his fiftieth birthday. While at Marburg, in the autumn of 1911, Wegener was browsing in the university library when he came across a scientific paper that listed fossils of identical plants and animals found on opposite sides of the Atlantic. Intrigued by this information, Wegener began to look for, and find, more cases of similar organisms separated by great oceans. Orthodox science at the time explained such cases by postulating that land bridges, now sunken, had once connected far-flung continents.

But Wegener noticed the close fit between the coastlines of Africa and South America. Might the similarities among organisms be due, not to land bridges, but to the continents having been joined together at one time? As he later wrote: "A conviction of the fundamental soundness of the idea took root in my mind." Such an insight, to be accepted, would require large amounts of supporting evidence. Wegener found that large-scale geological features on separated continents often matched very closely when the continents were brought together. For example, the Appalachian mountains of eastern North America matched with the Scottish Highlands, and the distinctive rock strata of the Karroo system of South Africa were identical to those of the Santa Catarina system in Brazil. Wegener also found that the fossils found in a certain place often indicated a climate utterly different from the climate of today: for example, fossils of tropical plants, such as ferns and cycads, are found today on the Arctic island of Spitsbergen.

All of these facts supported Wegener's theory of "continental drift." In 1915 the first edition of The Origin of Continents and Oceans, a book outlining Wegener's theory, was published; expanded editions were published in 1920, 1922, and 1929. About 300 million years ago, claimed Wegener, the continents had formed a single mass, called Pangaea (from the Greek for "all the Earth"). Pangaea had rifted, or split, and its pieces had been moving away from each other ever since. Wegener was not the first to suggest that the continents had once been connected, but he was the first to present extensive evidence from several fields. Modern reconstruction of Pangaea, ca. 255 million years ago -- click to view a much larger version of this map! Reaction to Wegener's theory was almost uniformly hostile, and often exceptionally harsh and scathing; Dr. Rollin T.

Chamberlin of the University of Chicago said, "Wegener's hypothesis in general is of the footloose type, in that it takes considerable liberty with our globe, and is less bound by restrictions or tied down by awkward, ugly facts than most of its rival theories." Part of the problem was that Wegener had no convincing mechanism for how the continents might move. Wegener thought that the continents were moving through the earth's crust, like icebreakers plowing through ice sheets, and that centrifugal and tidal forces were responsible for moving the continents. Opponents of continental drift noted that plowing through oceanic crust would distort continents beyond recognition, and that centrifugal and tidal forces were far too weak to move continents -- one scientist calculated that a tidal force strong enough to move continents would cause the Earth to stop rotating in less than one year. Another problem was that flaws in Wegener's original data caused him to make some incorrect and outlandish predictions: he suggested that North America and Europe were moving apart at over 250 cm per year (about ten times the fastest rates seen today, and about a hundred times faster than the measured rate for North America and Europe).

There were scientists who supported Wegener: the South African geologist Alexander Du Toit supported it as an explanation for the close similarity of strata and fossils between Africa and South America, and the Swiss geologist Émile Argand saw continental collisions as the best explanation for the folded and buckled strata that he observed in the Swiss Alps. Wegener's theory found more scattered support after his death, but the majority of geologists continued to believe in static continents and land bridges. What prompted the revival of continental drift ? In large part it was increased exploration of the Earth's crust, notably the ocean floor, beginning in the 1950s and continuing on to the present day. By the late 1960s, plate tectonics was well supported and accepted by almost all geologists. We now know that Wegener's theory was wrong in one major point: continents do not plow through the ocean floor. Instead, both continents and ocean floor form solid plates, which "float" on the asthenosphere , the underlying rock that is under such tremendous heat and pressure that it behaves as an extremely viscous liquid.

(Incidentally, this is why the older term "continental drift" is not quite accurate -- both continents and oceanic crust move.) Since Wegener's day, scientists have mapped and explored the great system of oceanic ridges, the sites of frequent earthquakes, where molten rock rises from below the crust and hardens into new crust. We now know that the farther away you travel from a ridge, the older the crust is, and the older the sediments on top of the crust are. The clear implication is that the ridges are the sites where plates are moving apart (click on the picture at the left to see a map of the age of the ocean crust). Where plates collide, great mountain ranges may be pushed up, such as the Himalayas; or if one plate sinks below another, deep oceanic trenches and chains of volcanoes are formed. Earthquakes are by far most common along plate boundaries and rift zones: plotting the location of earthquakes allows seismologists to map plate boundaries and depths (click on the picture at the right to view a map of quake epicenters). Paleomagnetic data have allowed us to map past plate movements much more precisely than before.

It is even possible to measure the speed of continental plates extremely accurately, using satellite technology. Nevertheless, Wegener's basic insights remain sound, and the lines of evidence that he used to support his theory are still actively being researched and expanded. The images of the ocean floor on this page were provided by the World Data Center A of the National Geophysical Data Center/ NOAA. There are a number of excellent WWW sites dealing with the modern theory of plate tectonics. Here is a modest sample: Alfred Wegener | Earth 520: Plate Tectonics and People: Foundations of Solid Earth Science Print Biographical Information Alfred Wegener was born on November 1, 1880 in Berlin. He was the son of an evangelical minister. Ironically, Wegener was not schooled in geology. He earned his doctorate in Astronomy. However, Wegener's true passions were in the fields of meteorology and arctic exploration. Wegener married Elsa Koppen, daughter of meteorologist Wladimir Peter Koppen in 1913. He succeeded Koppen as the director of the Meteorological Research Department of the Marine Observatory at Hamburg after World War I.

In 1924, he became the chair of the meteorology and geophysics department at the University of Graz in Austria. Wegener was somewhat of an adventurous spirit. One of his primary ambitions was arctic exploration, particularly in Greenland. Wegener took three trips to Greenland in his lifetime. His second trip in 1912 featured the longest crossing of an ice cap ever taken at the time and resulted in the publication of multiple glaciological and meteorological volumes. Wegener died in 1930 of a heart attack caused by overexertion while leading his third expedition in Greenland. Specific contributions to plate tectonic theory- Continental Drift One could say that Alfred Wegener is the father of Plate Tectonic Theory. Wegener noticed that the east coast of South America lined up almost perfectly with the west coast of Africa. This was certainly not a new observation. In 1620, Francis Bacon called attention to the similarities in the continental outlines of eastern South America and western Africa. In 1858, Antonio Snider-Pelligrini suggested that the continents had been moved by the biblical flood. Wegener's assessment sticks out for two reasons.

The first reason Wegener's hypothesis holds weight is that Wegener used geological evidence to back his claim that Africa and South America were at one time connected. The collection of maps, rock formations, and fossil records provided the evidence Wegener needed to connect South America to Africa. Most people observed the apparent surface similarities of the two coasts, but Wegener was the first to look into how the continents fit together at their respective continental shelves. The continental shelf is the shallow ocean lying off the coast of a continent. Wegener compared the outlines of South America's eastern continental shelf with Africa's western continental shelf. It turned out that the continental shelves of the two continents fit together even better than the observable coastlines. This was the first step for Wegener connecting the two continents (scientifically). Next, Wegener used geologic and fossil records to further support his claim. Wegener noticed that fossils from a small lizard from the Paleozoic Era (approx. 270 million years ago) appeared in only two places on Earth. Fossils for the Mesosaurus are found only in southern Africa and eastern South America. The Mesosaurus was a freshwater animal and would be incapable of crossing the Atlantic Ocean.

This would lend credence to the belief that Africa and South America were connected 270 million years ago when the Mesosaurus roamed the Earth. Wegener also tried to provide a viable mechanism for continental movement, but this posed problems. The leading theory of the time was that the earth formed in a molten state. The heavy elements sunk to the core while the lighter elements floated to the surface and cooled to form the crust. The thought was that mountains and oceans were caused by shrinkage. That is, the earth contracted as it cooled. Wegener discredited this hypothesis on the grounds that mountains and valleys don't form in uniform patterns. He also observed that the earths crust had two basic elevations. These elevations were the ocean abyss and the contiental crust. This observation would not provide Wegener with the engine for continental drift, but it would be a pivotal point of study for future scientists and would lead to theories in sea floor spreading and, ultimately, plate tectonic theory. Other interesting scientific contributions 1.) Alfred Wegener observed the apparent wandering of earth's magnetic pole. Wegener attributed this to the movement of the poles followed the approximate path of the movement of his continents.

Not only did this discovery provide evidence of continental drift, it also was an early example of the study of paleomagnetism. 2.) Wegener also used paleo climatology to help prove his theories. He used fossil records to study climate change through geologic time. Paleoclimatology is currently a hot field in science, as scientists attempt to determine the potential effects of greenhouse gas emissions caused by human activity. Other cool stuff you should know 1.) In 1906, Wegener and his brother Kurt set a world record for uninterrupted balloon flight at 52 hours. 2.) Geology and paleoclimatology, and paleomagnetism were the sciences that Wegener used to formulate his Continental Drift hypothesis, but Wegener was not officially schooled in any of them. Wegener's doctorate was in Astronomy. However, Wegener's livelihood came mostly from the field of meteorology. 3.) Wegener was a lifelong smoker. His death in 1930 of heart failure due to overexertion is often attributed to his smoking habit. 4.) Continental drift did not gain popular acceptance until the 1960s. One issue was Wegener's lack of geoscience credentials.

Another issue that hurt the hypothesis was the mechanism that Wegener proposed to initiate continental drift. Wegener believed that tides in the crust caused continental drift, but this idea was defeated by Harold Jeffries who proved that these proposed tides were not strong enough to cause continental drift. He also pointed out that Wegener's hypothesis did not account for verticle movement in the earth's crust. It was not until Harry Hess proposed the theory of sea floor spreading based on mid ocean ridges that the continental drift theory would get its engine. Bibliography 1. 2. ~lstrayer/geol2101/2101_Ch19_03.pdf 3. Hallam, A. Alfred Wegener and the Hypothesis of Continental Drift. Scientific American. 232(2). 1975 pp 88-97 Continental Drift and Plate-Tectonics Theory Continental Drift and Plate-Tectonics Theory Source: U.S. Dept. of the Interior, Geological Survey According to the theory of continental drift , the world was made up of a single continent through most of geologic time. That continent eventually separated and drifted apart, forming into the seven continents we have today.

The first comprehensive theory of continental drift was suggested by the German meteorologist Alfred Wegener in 1912. The hypothesis asserts that the continents consist of lighter rocks that rest on heavier crustal material—similar to the manner in which icebergs float on water. Wegener contended that the relative positions of the continents are not rigidly fixed but are slowly moving—at a rate of about one yard per century. According to the generally accepted plate-tectonics theory , scientists believe that Earth's surface is broken into a number of shifting slabs or plates, which average about 50 miles in thickness. These plates move relative to one another above a hotter, deeper, more mobile zone at average rates as great as a few inches per year. Most of the world's active volcanoes are located along or near the boundaries between shifting plates and are called plate-boundary volcanoes. The peripheral areas of the Pacific Ocean Basin, containing the boundaries of several plates, are dotted with many active volcanoes that form the so-called Ring of Fire. The Ring provides excellent examples of plate-boundary volcanoes, including Mount St. Helens.

However, some active volcanoes are not associated with plate boundaries, and many of these so-called intra-plate volcanoes form roughly linear chains in the interior of some oceanic plates. The Hawaiian Islands provide perhaps the best example of an intra-plate volcanic chain, developed by the northwest-moving Pacific plate passing over an inferred “hot spot” that initiates the magma-generation and volcano-formation process. Plate-Tectonics Theory—The Lithosphere Plates of Earth This figure shows the boundaries of lithosphere plates that are active at present. The double lines indicate zones of spreading from which plates are moving apart. The lines with barbs show zones of underthrusting (subduction), where one plate is sliding beneath another. The barbs on the lines indicate the overriding plate. The single line defines a strike-slip fault along which plates are sliding horizontally past one another. The stippled areas indicate a part of a continent, exclusive of that along a plate boundary, which is undergoing active extensional, compressional, or strike-slip faulting. Source: U.S. Geological Survey.

Historical perspective [This Dynamic Earth, USGS] Tectonic plates [115 k] The belief that continents have not always been fixed in their present positions was suspected long before the 20th century; this notion was first suggested as early as 1596 by the Dutch map maker Abraham Ortelius in his work Thesaurus Geographicus. Ortelius suggested that the Americas were "torn away from Europe and Africa . . . by earthquakes and floods" and went on to say: "The vestiges of the rupture reveal themselves, if someone brings forward a map of the world and considers carefully the coasts of the three [continents]." Ortelius' idea surfaced again in the 19th century. However, it was not until 1912 that the idea of moving continents was seriously considered as a full-blown scientific theory -- called Continental Drift -- introduced in two articles published by a 32-year-old German meteorologist named Alfred Lothar Wegener. He contended that, around 200 million years ago, the supercontinent Pangaea began to split apart.

Alexander Du Toit, Professor of Geology at Witwatersrand University and one of Wegener's staunchest supporters, proposed that Pangaea first broke into two large continental landmasses, Laurasia in the northern hemisphere and Gondwanaland in the southern hemisphere. Laurasia and Gondwanaland then continued to break apart into the various smaller continents that exist today. In 1858, geographer Antonio Snider-Pellegrini made these two maps showing his version of how the American and African continents may once have fit together, then later separated. Left: The formerly joined continents before (avant) their separation. Right: The continents after (aprés) the separation. (Reproductions of the original maps courtesy of University of California, Berkeley.) Wegener's theory was based in part on what appeared to him to be the remarkable fit of the South American and African continents, first noted by Abraham Ortelius three centuries earlier. Wegener was also intrigued by the occurrences of unusual geologic structures and of plant and animal fossils found on the matching coastlines of South America and Africa, which are now widely separated by the Atlantic Ocean.

He reasoned that it was physically impossible for most of these organisms to have swum or have been transported across the vast oceans. To him, the presence of identical fossil species along the coastal parts of Africa and South America was the most compelling evidence that the two continents were once joined. In Wegener's mind, the drifting of continents after the break-up of Pangaea explained not only the matching fossil occurrences but also the evidence of dramatic climate changes on some continents. For example, the discovery of fossils of tropical plants (in the form of coal deposits) in Antarctica led to the conclusion that this frozen land previously must have been situated closer to the equator, in a more temperate climate where lush, swampy vegetation could grow. Other mismatches of geology and climate included distinctive fossil ferns (Glossopteris) discovered in now-polar regions, and the occurrence of glacial deposits in present-day arid Africa, such as the Vaal River valley of South Africa. The theory of continental drift would become the spark that ignited a new way of viewing the Earth. But at the time Wegener introduced his theory, the scientific community firmly believed the continents and oceans to be permanent features on the Earth's surface.

Not surprisingly, his proposal was not well received, even though it seemed to agree with the scientific information available at the time. A fatal weakness in Wegener's theory was that it could not satisfactorily answer the most fundamental question raised by his critics: What kind of forces could be strong enough to move such large masses of solid rock over such great distances? Wegener suggested that the continents simply plowed through the ocean floor, but Harold Jeffreys, a noted English geophysicist, argued correctly that it was physically impossible for a large mass of solid rock to plow through the ocean floor without breaking up. Rejoined continents [48 k] Undaunted by rejection, Wegener devoted the rest of his life to doggedly pursuing additional evidence to defend his theory. He froze to death in 1930 during an expedition crossing the Greenland ice cap, but the controversy he spawned raged on. However, after his death, new evidence from ocean floor exploration and other studies rekindled interest in Wegener's theory, ultimately leading to the development of the theory of plate tectonics.

Plate tectonics has proven to be as important to the earth sciences as the discovery of the structure of the atom was to physics and chemistry and the theory of evolution was to the life sciences. Even though the theory of plate tectonics is now widely accepted by the scientific community, aspects of the theory are still being debated today. Ironically, one of the chief outstanding questions is the one Wegener failed to resolve: What is the nature of the forces propelling the plates? Scientists also debate how plate tectonics may have operated (if at all) earlier in the Earth's history and whether similar processes operate, or have ever operated, on other planets in our solar system. Continental Drift Hypothesis - Tectonophysics - Great Rift Valley -Crystalinks Continental Drift Hypothesis Continental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912 when he noticed that the shapes of continents on either side of the Atlantic Ocean seem to fit together (for example, Africa and South America).

Francis Bacon, Antonio Snider-Pellegrini, Benjamin Franklin, and others had noted much the same thing earlier. However, it was not until the development of the theory of plate tectonics in the 1960s, that a sufficient geological explanation of that movement was found. The similarity of southern continent fossil faunas and some geological formations had led a relatively small number of Southern hemisphere geologists to conjecture as early as 1900 that all the continents had once been joined into a supercontinent known as Pangaea. The concept was initially ridiculed by most geologists, who felt that an explanation of how a continent drifted was a prerequisite and that the lack of one made the idea of drifting continents wholly unreasonable. The theory received support through the controversial years from South African geologist Alexander Du Toit as well as from Arthur Holmes. The idea of continental drift did not become widely accepted as theory until the 1950s in Europe. By the 1960s, geological research conducted by Robert Dietz, Bruce Heezen, and Harry Hess along with a rekindling of the theory including a mechanism by J. Tuzo Wilson led to acceptance among North American geologists.

The hypothesis of continental drift became part of the larger theory of plate tectonics. This article deals mainly with the historical development of the continental drift hypothesis before 1950. Evidence for the movement of continents on tectonic plates is now extensive. Similar plant and animal fossils are found around the shores of different continents, suggesting that they were once joined. The fossils of Mesosaurus, a freshwater reptile rather like a small crocodile, found both in Brazil and South Africa, are one example; another is the discovery of fossils of the land reptile Lystrosaurus in rocks of the same age at locations in Africa, India, and Antarctica. There is also living evidence the same animals being found on two continents. Some earthworm families (e.g. Ocnerodrilidae, Acanthodrilidae, Octochaetidae) are found in South America and Africa, for instance. The complementary arrangement of the facing sides of South America and Africa is obvious, but is a temporary coincidence. In millions of years, slab pull and ridge-push, and other forces of tectonophysics, will further separate and rotate those two continents.

It was this temporary feature which inspired Wegener to study what he defined as continental drift, although he did not live to see his hypothesis generally accepted. Widespread distribution of Permo-Carboniferous glacial sediments in South America, Africa, Madagascar, Arabia, India, Antarctica and Australia was one of the major pieces of evidence for the theory of continental drift. The continuity of glaciers, inferred from oriented glacial striations and deposits called tillites, suggested the existence of the supercontinent of Gondwana, which became a central element of the concept of continental drift. Striations indicated glacial flow away from the equator and toward the poles, based on continents' current positions and orientations, and supported the idea that the southern continents had previously been in dramatically different locations, as well as being contiguous with each other. Continental Drift Hypothesis Development of Tectonophysics The evolution of tectonophysics is closely linked to the history of the continental drift and plate tectonics hypotheses. The continental drift hypothesis had many flaws and scarce data. The fixist, the contracting Earth and the expanding Earth concepts had many flaws as well. Wegener had data for assuming that the relative positions of the continents change over time.

It was a mistake to state the continents "plowed" through the sea. He was an outsider with a doctorate in astronomy attacking a established theory between geophysicists. The geophysicists were right to state that the Earth is solid, and the mantle is elastic (for seismic waves) and inhomogeneous, and the ocean floor would not allow the movement of the continents. But excluding one alternative, substantiates the opposite alternative: passive continents and an active seafloor spreading and subduction, with accretion belts on the edges of the continents. The velocity of the sliding continents, was allowed in the uncertainty of the fixed continent model and seafloor subduction and upwelling with phase change allows for inhomogeneity. The problem too, was the specialization. A. Holmes and A. Rittmann saw it right (Rittmann 1939). Only an outsider can have the overview, only an outsider sees the forest, not only the trees (Hellman 1998b, p. 145). But A. Wegener did not have the specialization to correctly weight the quality of the geophysical data and the paleontologic data, and its conclusions.

Wegener's main interest was meteorology, and he wanted to join the Denmark-Greenland expedition scheduled for mid 1912. So he hurried up to present his Continental Drift hypothesis. Timeline of the Development of Tectonophysics The Great Rift Valley The Great Rift Valley is a name given in the late 19th century by British explorer John Walter Gregory to the continuous geographic trench, approximately 6,000 kilometres (3,700 mi) in length, that runs from northern Syria in Southwest Asia to central Mozambique in East Africa. The name continues in some usages, although it is today considered geologically imprecise as it combines features that are today regarded as separate, although related, rift and fault systems. Today, the term is most often used to refer to the valley of the East African Rift, the divergent plate boundary which extends from the Afar Triple Junction southward across eastern Africa, and is in the process of splitting the African Plate into two new separate plates. Geologists generally refer to these incipient plates as the Nubian Plate and the Somali Plate.

Breakup of supercontinent Pangea cooled mantle and thinned crust PhysOrg - December 13, 2016 The oceanic crust produced by the Earth today is significantly thinner than crust made 170 million years ago during the time of the supercontinent Pangea. The thinning is related to the cooling of Earth's interior prompted by the splitting of the supercontinent Pangaea, which broke up into the continents that we have today. The mantle is the very hot, but mostly solid, layer of rock between the Earth's crust and core. Magma from the mantle forms oceanic crust when it rises from the mantle to the surface at spreading centers and cools into the rock that forms the very bottom of the seafloor. Since about 2.5 billion years ago, the mantle has been cooling - a phenomenon that doesn't influence the climate on the surface of the Earth and has nothing to do with the issue of short-term man-made climate change. Texas and Antarctica Were Attached, Rocks Hint National Geographic - August 17, 2011 About 1.1 billion years ago, what are now El Paso, Texas, and Antarctica appear to have existed side by side, scientists say.

The find is part of a decades-long effort to piece together fragments of an ancient supercontinent that existed before Pangaea. "Most people are familiar with Pangaea," said study co-author Staci Loewy, a geochemist at California State University, Bakersfield. "That was a supercontinent that formed 300 million years ago." Pangaea began to break apart about 225 million years ago due to geological processes related to plate tectonics, which eventually spread Earth's landmasses into the continents we see today. The supercontinent's pieces can be reassembled by tracing ancient mountain belts and other geologic patterns - such as the Appalachian Mountains, which are geologically related to mountains of England and Scandinavia. Red Sea Region Parting in Massive Split National Geographic - July 19, 2006 Moses may have received some geological assistance when he parted the Red Sea to let the Israelites through, according to the Bible. In a new study, scientists have determined that a recent tear in Earth's continental crust near the sea is the largest single rip seen since satellite monitoring began.

Secrets of ocean birth laid bare BBC - July 20, 2006 The largest tear in the Earth's crust seen in decades, if not centuries, could carve out a new ocean in Africa, according to satellite data. Geologists say a crack that opened up last year may eventually reach the Red Sea, isolating much of Ethiopia and Eritrea from the rest of Africa. The 60km-long rift was initially sparked by an earthquake in September. Follow-up observations reported in the journal Nature suggest the split is growing at an unprecedented rate. Exodus From Drying Sahara Gave Rise to Pharaohs, Study Says National Geographic - July 20, 2006 Sahara Desert Was Once Lush and Populated -- The pharaohs of ancient Egypt owed their existence to prehistoric climate change in the eastern Sahara, according to an exhaustive study of archaeological data that bolsters this theory. Starting at about 8500 B.C., researchers say, broad swaths of what are now Egypt, Chad, Libya, and Sudan experienced a "sudden onset of humid conditions." How Did Continents Split?

Geology Study Shows New Picture PhysOrg - May 24, 2006 Like pieces in a giant jigsaw puzzle, continents have split, drifted and merged again many times throughout Earth's history, but geologists haven't understood the mechanism behind the moves. A new study now offers evidence that continents sometimes break along preexisting lines of weakness created when small chunks of land attach to a larger continent. continental drift | geology | Britannica.com Continental drift isostasy Continental drift, large-scale horizontal movements of continents relative to one another and to the ocean basins during one or more episodes of geologic time . This concept was an important precursor to the development of the theory of plate tectonics , which incorporates it. The changing Earth through geologic time, from the late Cambrian Period (c. 500 million years … Adapted from C.R. Scotese, The University of Texas at Arlington The idea of a large-scale displacement of continents has a long history. Noting the apparent fit of the bulge of eastern South America into the bight of Africa, the German naturalist Alexander von Humboldt theorized about 1800 that the lands bordering the Atlantic Ocean had once been joined.

Some 50 years later, Antonio Snider-Pellegrini , a French scientist, argued that the presence of identical fossil plants in both North American and European coal deposits could be explained if the two continents had formerly been connected, a relationship otherwise difficult to account for. In 1908 Frank B. Taylor of the United States invoked the notion of continental collision to explain the formation of some of the world’s mountain ranges. The first truly detailed and comprehensive theory of continental drift was proposed in 1912 by Alfred Wegener , a German meteorologist. Bringing together a large mass of geologic and paleontological data, Wegener postulated that throughout most of geologic time there was only one continent, which he called Pangea . Late in the Triassic Period (which lasted from approximately 251 million to 199.6 million years ago), Pangea fragmented, and the parts began to move away from one another. Westward drift of the Americas opened the Atlantic Ocean, and the Indian block drifted across the Equator to merge with Asia . In 1937 Alexander L.

Du Toit , a South African geologist, modified Wegener’s hypothesis by suggesting two primordial continents: Laurasia in the north and Gondwana in the south. A discussion of some of the evidence supporting continental drift on Earth. Encyclopædia Britannica, Inc. uplift Aside from the congruency of continental shelf margins across the Atlantic, modern proponents of continental drift have amassed impressive geologic evidence to support their views. Indications of widespread glaciation from 380 to 250 million years ago are evident in Antarctica , southern South America, southern Africa, India , and Australia . If these continents were once united around the south polar region, this glaciation would become explicable as a unified sequence of events in time and space. Also, fitting the Americas with the continents across the Atlantic brings together similar kinds of rocks, fossils, and geologic structures. A belt of ancient rocks along the Brazilian coast, for example, matches one in West Africa . Moreover, the earliest marine deposits along the Atlantic coastlines of either South America or Africa are Jurassic in age (approximately 199.6 million to 145.5 million years old), which suggests that the ocean did not exist before that time.

plate tectonics: Alfred Wegener and the concept of continental drift Interest in continental drift increased in the 1950s as knowledge of Earth’s geomagnetic field during the geologic past developed from the studies of the British geophysicists Stanley K. Runcorn , Patrick M.S. Blackett , and others. Ferromagnetic minerals such as magnetite acquire a permanent magnetization when they crystallize as constituents of igneous rock . The direction of their magnetization is the same as the direction of Earth’s magnetic field at the time and place of crystallization. Particles of magnetized minerals released from their parent igneous rocks by weathering may later realign themselves with the existing magnetic field at the time these particles are incorporated into sedimentary deposits. Studies by Runcorn of the remanent magnetism in suitable rocks of different ages from Europe produced a “polar wandering curve” indicating that the magnetic poles were in different places at different times. This could be explained either by the migration of the magnetic pole itself (that is, polar wandering ) or by the migration of Europe relative to a fixed pole (that is, continental drift). Rocks and Minerals: Fact or Fiction?

However, further work showed that the polar wandering curves are different for the various continents. The possibility that they might reflect true wander of the poles was discarded, because it implies separate wanderings of many magnetic poles over the same period. However, these different paths are reconciled by joining the continents in the manner proposed by Wegener. The curves for Europe and North America , for example, are reconciled by the assumption that the latter has drifted about 30° westward relative to Europe since the Triassic Period. Britannica Stories

Question: What is the name for the study of Continental Drift?
Answer: Plate Tectonics